DIY Russian Big Muff Mid Knob

[rthryhorysak]

I am building this Russian Big Muff, but I would prefer a Mid Knob, as opposed to a switch. Is there an easy replacement for the pot and how would I go about doing it?

[nocentelli]

Easiest way is to put a 10n cap from Q3 collector to tone3 (instead of the stock 4n cap in the layout) and replace the "tone3 to ground resistor" with a 100k pot in series with a small resistor  ( e.g. 4k7). On IvIark's layout, you could just leave off that 100k resistor, make a cut on the second row to the left of the 2k2 - Run the 4k7 from the tone3 row to the left of the new cut, run a wire from that row to lug 1 of the new mids pot, and connect mids2 to ground. Check out the amz presence control page for more information on this kind of mod:

http://www.muzique.com/lab/tone3.htm

It's probably a good idea to install duncan's tonestack simulator on your pc: Find the big muff circuit and play around with cap, resistor and pot values and learn how each part contributes to the degree of mid boost or scoop available - You can then try out your chosen values to hear if you like it before committing.

http://www.duncanamps.com/tsc/

[lmorse]

+1 for Duncan's Tone Stack. Great learning tool!

[rthryhorysak]

Ok I think I found an easier way to add the mid knob. So replace the 4n with a 12n or whatever value. Then take the 100k resistor from tone 3 to ground, and move the top leg down 1 row. Then make a cut after it and connect that row to mids 3 and mids 2 to ground. Thoughts?

[nocentelli]

That will only boost mids - swap the 100k in your description for something smaller, e.g. 4k7 or 10k to set the maximum scoop.

[digi2t]

Looking at the schematic posted, at the bottom of the tone section (boxed values); replace the 3.9nF cap with a 15nF. Replace the 22K resistor with a A25K pot, in series with a 3.3K resistor, to ground. Doesn't matter what order of the pot and resistor.

This will give you a close to original mid scoop at one end, and a slight mid hump at the other.